1. Technical Field
The present disclosure relates to a circuit and a method for controlling a total harmonic current distortion (THDi), in particular, to a THDi control circuit and method thereof.
2. Description of Related Art
A power factor (PF) represents the relationship between the effective or the real power and the apparent power. In other words, the power factor is defined as the ratio of the effective power to the apparent power. Basically, a power factor can be used to measure how efficient the electricity is being used. The larger the power factor is, the more efficiently the electricity is used.
A total harmonic current distortion (THDi) represents a distortion level of the current returning to the power grid. The higher the THDi is indicating the higher the distortion level, hence more damage to the power grid and the back-end equipment. High performance equipment generally has the range of the THDi clearly defined. Therefore, the THDi has become an important indicator for high performance equipment.
Power equipment or electronic devices such as power system for computers, LED power source circuit, uninterruptible power supply systems (UPS) and the like, generally are equipped with power factor correction circuits. Currently, there are many limitations to the performance of power factor correction circuits for small-capacity UPS applications (e.g., 1K˜6K UPS applications). For instance, when the power factor correction circuit provides a full-load output, the power factor correction circuit can only achieve low THDi (approximately 10%) within a small range of the AC power (e.g., 220V to 230V) supplied.
Furthermore, some UPSs adopt digital control and utilize advanced digital signal processors with powerful computational functionality to implement high performance power factor correction circuits. Although these digital types of UPSs are able to provide the same power factor correction results, but the relative costs and complexities of implementing the power factor correction circuits dramatically increases.